This invention relates to lubricating oils. In one of its aspects this invention relates to lubricating oils containing sulfur, particularly mercaptan sulfur. In another of its aspects this invention relates to a method for increasing the resistance to oxidation of petroleum lubricating oil.
Lubricatng oil, particularly in high temperature service, is susceptible to destructive oxidation unless it has been treated with an oxidation inhibitor--generally a zinc compound. This treatment is costly and also increases the sulfated ash concentration of the oil. The sulfated ash concentration may be subject to legislative control in the future.
It is therefore an object of this invention to provide a method for increasing the resistance to oxidation of petroleum lubricating oil without significantly affecting its sulfated ash content. It is another object of this invention to provide a treated lubricating oil of increased resistance to oxidation that does not have a significantly increased sulfated ash content.
Other aspects, objects and the various advantages of this invention will become apparent upon reading this specification and the appended claims.